The company behind plans for a wind farm on land near Lyveden New Bield in Northamptonshire has taken its case to the Court of Appeal.
West Coast Energy is trying to overturn a decision made at the High Court in March.
It wants to build four 300ft (91.4m) turbines on the Barnwell Manor estate, Sudborough.
The National Trust says the proposal is too close to Lyveden New Bield, a 17th Century lodge.
The evidence has now been heard and the Lord Justices are expected to consider the case over the next fortnight.
Plans for five turbines at Barnwell Manor were rejected by East Northamptonshire District Council in 2010 following local opposition.
But the developers won an appeal for four turbines, before this was overturned by Mrs Justice Lang at the High Court.
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